Production of proteins of biological interest has been, in recent years, a primary goal of the genetic engineering field. The present inventors have developed a method for producing such proteins through the use of "transhybridomas," i.e., hybridomas produced using lymphocytes of transgenic animals.
The ability to introduce foreign genes into mammalian embryos has been recently developed. This method for the creation of so-called "transgenic" animals has allowed increased study of gene regulation and the genetic basis for development. To develop a transgenic animal, foreign DNA is introduced into the mammalian genome by micro-injection of DNA molecules into the pronuclei of fertilized eggs. The fertilized eggs are then inserted into the reproductive tracts of foster mothers and continue to develop there, eventually resulting in the birth of the transgenic animals. Because integration of the foreign DNA into the mammalian chromosome occurs at an early stage in embryo development, there is ubiquitous transfer of the foreign DNA throughout the germ line.
Various researchers have described the basic process for the creation of transgenic animals, particularly mice. For example, Palmiter et al., in "Dramatic Growth of Mice That Develop From Eggs Microinjected with Metallothionein-Growth Hormone Fusion Genes," Nature. Vol. 300, 611-615 (Dec. 1982). Alt et al., have summarized some features of immunoglobulin genes in transgenic mice In Trends In Genetics, Aug., 1985, pp. 231-236. Both of these papers, which are specifically incorporated herein by reference, describe these processes.
As indicated by the title of the article, Palmiter et al. discloses the integration of a metallothionein-rat growth hormone fusion gene into the mouse genome, observing rapid growth of the resultant transgenic mice. On the other hand, Alt et al. reported the production of a transgenic mouse expressing a mouse immunoglobulin transgene from the lymphocytes. In addition, lymphocytes, described by Ritchie et al. in Nature 312:517 (1986), have been made to synthesize murine immunoglobulins. However, these lymphocytes are cells which would normally synthesize the corresponding mouse immunoglobulins. Thus, to date, there have been no published reports in the literature of the in vitro expression, using cells obtained from transgenic animals, of gene products of human genes wherein the transgenic animal cell does not normally express an analogous animal gene product.
The present inventors, however, have succeeded in obtaining consistent, high levels of expression of human growth hormone, normally produced by pituitary cells, from transgenic mouse lymphocytes. In addition, the present inventors have developed a technique for the creation of certain hybridomas, hereinafter referred to as "transhybridomas." This method involves the fusion of a transgenic animal cell, which is producing a foreign gene product not analogous to a gene product normally produced by that cell, with an immortal cell line.
Using the method of the present invention and the transhybridoma that this method creates, it may be that large quantities of foreign gene products, especially proteins, can be obtained. In addition, through the use of a signal peptide, gene products which are not normally secreted from a cell may be produced and secreted from these transhybridomas, resulting in commercially-applicable processes and products for the production of useful proteins.